The present invention relates to decorative laminates bearing images printed on an interlayer by a process of ink jet printing. The present invention particularly relates to decorative laminates wherein the image has been printed onto an interlayer comprising polyvinyl butyral (PVB). The present invention also relates to ink formulations that are useful for preparing the laminates of the present invention.
Decorative laminates are known and obtained by various processes. DE 29706880, U.S. Pat. Nos. 4,968,553, 5,914,178, EP 1129844A1, and DE 20100717 disclose making decorative glass laminates via a silk screening process. Silk-screening an image onto an interlayer is a very time-consuming and expensive process for making decorative laminated safety glass. A process for making decorative glass laminates has also been described in U.S. Pat. No. 4,173,672. This patent describes a transfer lamination process wherein an image printed on paper is transferred to a thermoplastic film, and the film bearing the transferred image is then laminated between glass sheets.
Use of “ink jet” technology to print on PVB and polyurethanes for laminated safety glass has been disclosed in WO0218154. Ink jet printing is known and is a conventional process for printing wherein ink droplets are propelled through a printing head at a high speed towards a printing substrate. Ink jet technology is very flexible because any digital image can be printed onto a substrate.
However, one disadvantage of printing directly on PVB using an ink jet printing process is that PVB interlayers have a roughened surface pattern (Rz from 30-60 μm) that can cause poor image quality in a printed image. The roughened surface pattern is necessary in a PVB lamination process to obtain laminates free of air bubbles and other defects caused by the presence of trapped air during the lamination process. However, when ink jet printing onto PVB, the rough surface pattern can affect image quality with respect to mottle and resolution.
Other problems with conventional processes for ink-jet printing are encountered due to the inks used in conventional ink-jet processes. Low viscosity inks are required in a conventional ink jet printing process to alleviate high pressure build-up in the print head of the ink jet printer, and subsequent damage to the head and/or poor quality in the printed image. Ink jet printing is carried out conventionally by either (a) drop on demand (DOD) processes, such as a piezo electric printing or thermal ink jet printing processes, or (b) continuous drop ink jet printing. There are other factors as well that make low viscosity inks necessary and preferable in ink jet printing processes. However, use of conventional inks that are suitable for ink jet printing can result in poor image quality on a thermoplastic interlayer. Poor image quality can be the result when a low viscosity ink is sprayed onto a roughened surface such as a PVB surface that has been prepared for lamination, due to ink running from high points to low spots on the interlayer surface.
Another potential problem with printing an image on an interlayer prior to lamination onto another substrate is that the adhesive bond between the interlayer and the substrate can be significantly weakened due to colorant on the surface of the interlayer that can reduce the “effective” bonding surface area between the substrate and the interlayer. “Effective bonding surface” as used herein describes the surface area where the interlayer and the substrate are in direct contact with each other without an intervening colorant layer. Reduction of the adhesive force of the laminate can result in the laminate having poor performance as a safety glass, or in the application for which it was intended.
Still further problems can be encountered with ink jet printing onto thermoplastic polymer interlayer when the printed image requires both white and clear (that is, areas where there is no ink jetted onto the substrate) portions. In order to obtain an area where white appears in a printed image, current practice requires printing colored ink onto a white thermoplastic sheet. The white that appears in the image obtained in this manner results from the additive in the sheet, and not from printing a white pigment onto those areas where white is desirable in the printed image. This is not a practical solution when a clear (transparent) area is desirable together in the same image with a portion of white.
Ink jet printing a white pigment is not a known process. More particularly, no white ink system suitable for ink jet printing onto an interlayer material is known. Various factors make white ink systems problematical for ink-jet printing, but one problem can be the particle size of the white pigment used in the ink dispersion can be too large for ink-jet printing.
It can be desirable in a process for printing on thermoplastic interlayers prior to lamination, to have a process for ink jet printing white ink onto thermoplastic interlayers so that areas of white can be observed in an image or text, in addition to clear or transparent areas where no ink has been printed onto the substrate.
It can be particularly desirable to have such a process and maintain laminate strength and resilience against breakage, while at the same time producing a quality image on the interlayer substrate.